Power tool

ABSTRACT

A rotary hammer adapted to impart axial impacts to a tool bit. The rotary hammer includes a housing, a motor supported by the housing, a spindle coupled to the motor for receiving torque from the motor, causing the spindle to rotate, a reciprocation mechanism operable to create a variable pressure air spring within the spindle, an anvil received within the spindle for reciprocation in response to the pressure of the air spring, the anvil imparting axial impacts to the tool bit, a bit retention assembly for securing the tool bit to the spindle, and an electromagnetic clutch mechanism switchable between a first state, in which the reciprocation mechanism is enabled, such that the anvil imparts axial impacts to the tool bit, and a second state, in which the reciprocation mechanism is disabled, such that the anvil ceases to impart axial impacts to the tool bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. Provisional PatentApplication No. 63/003,995 filed on Apr. 2, 2020, the contents of whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to power tools, and more particularly topower tools including electromagnetic clutch mechanisms.

BACKGROUND OF THE INVENTION

Power tools can include a clutch mechanism to selectively permit apiston reciprocate in response to an impact mechanism receiving torquefrom a motor.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a rotary hammer adaptedto impart axial impacts to a tool bit. The rotary hammer includes ahousing, a motor supported by the housing, a spindle coupled to themotor for receiving torque from the motor, causing the spindle torotate, a reciprocation mechanism operable to create a variable pressureair spring within the spindle, an anvil received within the spindle forreciprocation in response to the pressure of the air spring, the anvilimparting axial impacts to the tool bit, a bit retention assembly forsecuring the tool bit to the spindle, and an electromagnetic clutchmechanism switchable between a first state, in which the reciprocationmechanism is enabled, such that the anvil imparts axial impacts to thetool bit, and a second state, in which the reciprocation mechanism isdisabled, such that the anvil ceases to impart axial impacts to the toolbit.

In some embodiments, the rotary hammer may further include a detectablemember on the spindle, a sensor on the housing and configured to detectwhether the detectable member is proximate or not proximate the sensor,and a controller configured to switch the electromagnetic clutchmechanism from the first state to the second state in response to thesensor detecting that the detectable member is not proximate the sensor.The spindle is moveable between a first position, in which the sensordetects that the detectable member is proximate the sensor, and a secondposition, in which the sensor detects that the detectable member is notproximate the sensor. And, the spindle is biased toward the secondposition.

In some embodiments, the detectable member is a washer.

The present invention provides, in another aspect, a rotary hammeradapted to impart axial impacts to a tool bit. The rotary hammerincludes a housing, a motor supported by the housing, a spindle coupledto the motor for receiving torque from the motor, causing the spindle torotate, and a reciprocation mechanism operable to create a variablepressure air spring within the spindle. The reciprocation mechanismincludes a piston disposed within the spindle, a crank gear receivingtorque from the motor, and a crank shaft configured to reciprocate thepiston within the spindle to create the variable pressure air spring inresponse to receiving torque from the crank gear. The rotary hammer alsoincludes an anvil received within the spindle for reciprocation inresponse to the pressure of the air spring, the anvil imparting axialimpacts to the tool bit, a bit retention assembly for securing the toolbit to the spindle, and an electromagnetic clutch mechanism switchablebetween a first state, in which the crank shaft receives torque from thecrank gear, such that the anvil imparts axial impacts to the tool bit,and a second state, in which the crank shaft does not receive torquefrom the crank gear, such that the anvil ceases to impart axial impactsto the tool bit.

The present invention provides, in another aspect, a rotary hammeradapted to impart axial impacts to a tool bit. The rotary hammerincludes a housing, a motor supported by the housing, a spindle coupledto the motor for receiving torque from the motor, causing the spindle torotate, and a reciprocation mechanism operable to create a variablepressure air spring within the spindle. The reciprocation mechanismincludes a piston disposed within the spindle, a crank gear receivingtorque from the motor, and a crank shaft configured to reciprocate thepiston within the spindle to create the variable pressure air spring inresponse to receiving torque from the crank gear. The rotary hammer alsoincludes an anvil received within the spindle for reciprocation inresponse to the pressure of the air spring, the anvil imparting axialimpacts to the tool bit, a bit retention assembly for securing the toolbit to the spindle, and a port in one of the spindle or the piston, anda closure member that is movable relative to the port between a firstposition, in which the closure member seals the port and an interiorvolume of the spindle between the piston the anvil is sealed to developthe variable pressure air spring, and a second position, in which theclosure member is spaced apart from the port and the interior volume ofthe spindle between the piston and the anvil is unsealed and unable todevelop the variable pressure air spring.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a rotary hammer having anelectromagnetic clutch according to an embodiment of the invention.

FIG. 2A is an enlarged cross-sectional view of the rotary hammer of FIG.1 with a spindle in a first position.

FIG. 2B is an enlarged cross-sectional view of the rotary hammer of FIG.1 with a spindle in a second position.

FIG. 3A is a perspective view of a crank gear and a crank shaft of FIG.1.

FIG. 3B is a cross-sectional view of the crank gear and the crank shaftof FIG. 1 along the line 3B-3B.

FIG. 4A is a perspective view of the crank gear and the crank shaft ofFIG. 1 and an electromagnetic clutch mechanism according to oneembodiment.

FIG. 4B is a cross-sectional view of the crank gear, the crank shaft,and the electromagnetic clutch mechanism of FIG. 4A along the line4B-4B.

FIG. 4C is an exploded view of the crank gear, the crank shaft, and theelectromagnetic clutch mechanism of FIG. 4A.

FIG. 4D is a cross-sectional view of the crank gear, the crank shaft,and the electromagnetic clutch mechanism of FIG. 4A along the line 4D-4D(shown in FIG. 4B), with the electromagnetic clutch mechanism in a firststate.

FIG. 4E is another cross-sectional view of the crank gear, the crankshaft, and the electromagnetic clutch mechanism of FIG. 4A along theline 4D-4D (shown in FIG. 4B), with the electromagnetic clutch mechanismin a second state.

FIG. 5A is a perspective view of the crank gear and the crank shaft ofFIG. 1 and an electromagnetic clutch mechanism according to anotherembodiment.

FIG. 5B is a cross-sectional view of the crank gear, the crank shaft,and the electromagnetic clutch mechanism of FIG. 5A along the line5B-5B.

FIG. 5C is an exploded view of the crank gear, the crank shaft, and theelectromagnetic clutch mechanism of FIG. 5A.

FIG. 5D is a cross-sectional view of the crank gear, the crank shaft,and the electromagnetic clutch mechanism of FIG. 5A along the line 5D-5D(shown in FIG. 5B), with the electromagnetic clutch mechanism in a firststate.

FIG. 5E is another cross-sectional view of the crank gear, the crankshaft, and the electromagnetic clutch mechanism of FIG. 5A along theline 5D-5D (shown in FIG. 5B), with the electromagnetic clutch mechanismin a second state.

FIG. 5F is a detailed cross-sectional view of the crank gear, the crankshaft, and the electromagnetic clutch mechanism of FIG. 5A along theline 5D-4D (shown in FIG. 5A).

FIG. 6 is a plan view of an electromagnetic clutch mechanism of a rotaryhammer according to another embodiment of the invention, with theelectromagnetic clutch mechanism in a first state.

FIG. 7 is a plan view of the electromagnetic clutch mechanism of FIG. 6,with the electromagnetic clutch mechanism in a second state.

FIG. 8 is a plan view of an electromagnetic clutch mechanism of a rotaryhammer according to another embodiment of the invention, with theelectromagnetic clutch mechanism in a first state.

FIG. 9 is a plan view of the electromagnetic clutch mechanism of FIG. 8,with the electromagnetic clutch mechanism in a second state.

FIG. 10 is a perspective view of an electromagnetic clutch mechanism ofa rotary hammer according to another embodiment of the invention.

FIG. 11 is an exploded view of an electromagnetic clutch mechanism of arotary hammer according to another embodiment of the invention

FIG. 12 is a perspective view of a coupler of the electromagnetic clutchmechanism of FIG. 11.

FIG. 13 is a perspective view of an electromagnetic clutch mechanism ofa rotary hammer according to another embodiment of the invention.

FIG. 14 is a cross-sectional view of an electromagnetic clutch mechanismof a rotary hammer according to another embodiment of the invention.

FIG. 15 is a cross-sectional view of an electromagnetic clutch mechanismof a rotary hammer according to another embodiment of the invention.

FIG. 16 is a perspective view of a crank gear and crank shaft of arotary hammer, according to another embodiment of the invention.

FIG. 17 is a plan view of a crank shaft of a rotary hammer according toanother embodiment of the invention.

FIG. 18 is a perspective view of a spindle of a rotary hammer accordingto another embodiment of the invention.

FIG. 19 is a perspective view of a coupler of the rotary hammerembodiment of FIG. 18.

FIG. 20 is a cross-sectional view of the rotary hammer embodiment ofFIG. 18.

FIG. 21 is a cross-sectional view of a rotary hammer according toanother embodiment of the invention.

FIG. 22 is a cross-sectional view of a rotary hammer according toanother embodiment of the invention.

FIG. 23 is a cross-sectional view of an electromagnetic clutch mechanismof a rotary hammer according to another embodiment of the invention.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates a reciprocating percussive power tool, such as rotaryhammer 10, according to an embodiment of the invention. The rotaryhammer 10 includes a housing 14, a motor 18 disposed within the housing14, and a rotatable spindle 22 coupled to the motor 18 for receivingtorque from the motor 18. In the illustrated construction, the rotaryhammer 10 includes a quick-release mechanism 24 coupled for co-rotationwith the spindle 22 to facilitate quick removal and replacement of atool bit 25. The tool bit 25 includes a groove 25 a in which a detentmember 26 of the quick-release mechanism 24 is received to constrainaxial movement of the tool bit 25 to the length of the groove 25 a. Therotary hammer 10 defines a tool bit axis 27, which in the illustratedembodiment is coaxial with a rotational axis 28 of the spindle 22.

In the illustrated embodiment, the motor 18 is configured as a DC motorthat receives power from an on-board power source 29 (e.g., a battery).The battery may include any of a number of different nominal voltages(e.g., 12V, 18V, etc.), and may be configured having any of a number ofdifferent chemistries (e.g., lithium-ion, nickel-cadmium, etc.). In someembodiments, the battery is a battery pack removably coupled to thehousing. In other embodiments, the motor 18 may be powered by a remotepower source (e.g., a household electrical outlet) through a power cord(not shown). The motor 18 is selectively activated by depressing anactuating member, such as a trigger 30, which in turn actuates anelectrical switch. The switch is electrically connected to the motor 18via a top-level or master controller 31 (shown schematically in FIGS.1-3), or one or more circuits, for controlling operation of the motor18.

The rotary hammer 10 further includes an impact mechanism 32 having areciprocating piston 34 disposed within the spindle 22, a striker 38that is selectively reciprocable within the spindle 22 in response toreciprocation of the piston 34, and an anvil 42 that is impacted by thestriker 38 when the striker 38 reciprocates toward the tool bit 25.Torque from the motor 18 is transferred to the spindle 22 by atransmission 46. In the illustrated construction of the rotary hammer10, the transmission 46 includes an input gear 50 engaged with a pinion54 on an output shaft 58 of the motor 18, an intermediate pinion 62coupled for co-rotation with the input gear 50 and an output gear 66coupled for co-rotation with the spindle 22 and engaged with theintermediate pinion 62. The output gear 66 is secured to the spindle 22using a spline-fit or a key and keyway arrangement, for example, thatfacilitates axial movement of the spindle 22 relative to the output gear66 yet prevents relative rotation between the spindle 22 and the outputgear 66. A clutch mechanism 70 is incorporated with the input gear 50 tolimit the amount of torque that may be transferred from the motor 18 tothe spindle 22.

With reference to FIGS. 1 and 3A-3B, the impact mechanism 32 is drivenby a crank gear 78 that is rotatably supported within the housing 14 ona stationary shaft 82, which defines a central axis 86 that is offsetfrom a rotational axis 90 of the output shaft 58 and pinion 54. As shownin FIG. 1, the respective axes 86, 90 of the stationary shaft 82 andoutput shaft 58 are parallel. Likewise, respective axes 90, 98 of theoutput shaft 58 and the intermediate pinion 62 are also parallel. Theimpact mechanism 32 also includes a crank shaft 102 rotatably supportedon the stationary shaft 82 and having an eccentric pin 110. The impactmechanism 32 further includes a connecting rod 116 interconnecting thepiston 34 and the eccentric pin 110.

The rotary hammer 10 includes an electromagnetic clutch mechanism 118arranged between and/or proximate the crank gear 78 and crank shaft 102,as shown in FIGS. 1 and 3A-3B. The electromagnetic clutch mechanism 118is switchable between a first state, in which the crank shaft 102 iscoupled for rotation with the crank gear 78, and a second state, inwhich the crank shaft 102 is disengaged from and/or decoupled forrotation with the crank gear 78. The electromagnetic clutch mechanism118 includes an electromagnet that is energized to move, or de-energizedto allow movement of, a magnetic component directly or indirectlycoupled to one of the crank gear 78 and the crank shaft 102. In someembodiments, the electromagnetic clutch mechanism 118 is one of theelectromagnetic clutch mechanisms described in U.S. patent applicationSer. No. 16/158,716 (“the '716 Application”) filed on Oct. 12, 2018, nowpublished as U.S. Publication No. 2019-0118362, the entire content ofwhich is incorporated herein by reference.

In some embodiments, the rotary hammer 10 includes a braking member or abraking surface arranged proximate the crank shaft 102, such that whenthe electromagnetic clutch mechanism 118 is switched to the second stateand the crank shaft 102 is disengaged from and/or decoupled for rotationwith the crank gear 78, the crank shaft 102 is brought into contact withthe braking member or braking surface and thus, the rotation of thecrank shaft 102 about the central axis 86 is rapidly decelerated. Inother embodiments, such a braking member or braking surface arrangedproximate the crank shaft 102 may be omitted.

As shown in FIGS. 1-2B, the rotary hammer 10 includes a sensor 122(shown schematically) configured to detect whether a detectable member,such as a washer 126 arranged on the spindle 22, is proximate the sensor122. In some embodiments, the sensor 122 may be configured as aHall-effect, force, proximity, or contact sensor or switch. The spindle22 is axially moveable between a first position (FIG. 2A), in which thewasher 126 is abutting or proximate the sensor 122, and a secondposition (FIG. 2B), in which the washer 126 is not proximate (e.g.,spaced apart from) the sensor 122, such that a gap G exists between thewasher 126 and the sensor 122. In some embodiments, the gap G is between1 millimeter and 3 millimeters. The spindle 22 is biased toward thesecond position by, for example, a spring (not shown).

The controller 31 is electrically connected with the motor 18, thesensor 122, and the electromagnet of the electromagnetic clutchmechanism 118. During operation of the rotary hammer 10 and when thetool bit 25 is engaged against a workpiece, the normal force from theworkpiece is translated through the tool bit 25 and anvil 42 to thespindle 22, such that the spindle 22 is pushed to the first position(shown in FIG. 2) against the biasing force of the spring. In responseto the sensor 122 detecting that the washer 126 is proximate the sensor122, the controller 31 allows the electromagnetic clutch mechanism 118to remain in the first state, such that the crank shaft 102 is coupledfor rotation with the crank gear 78 to enable the impact mechanism 32,causing reciprocation of the piston 34. If, during operation of therotary hammer 10, the tool bit 25 is removed from the workpiece, thespring biases the spindle 22 to the second position, thereby creatingthe gap G between the sensor 122 and the washer 126 (shown in FIG. 3).In response to the sensor 122 detecting that the washer 126 is notproximate the sensor 122, the controller 31 causes the electromagneticclutch mechanism 118 to switch from the first state to the second state,disabling the impact mechanism 32 and ceasing reciprocation of thepiston 34, as described in further detail below.

With reference to FIG. 1, the rotary hammer 10 includes a mode selectionmember 130 rotatable by an operator to switch between three modes. In a“hammer-drill” mode, the motor 18 is drivably coupled to the piston 34for reciprocating the piston 34 while the spindle 22 rotates. In a“drill-only” mode, the piston 34 is decoupled from the motor 18 but thespindle 22 is rotated by the motor 18. In a “hammer-only” mode, themotor 18 is drivably coupled to the piston 34 for reciprocating thepiston 34 but the spindle 22 does not rotate.

In operation, an operator selects either hammer-drill mode or drill-onlymode with the mode selection member 130. The operator then presses thetool bit 25 against the workpiece and depresses the trigger 30 toactivate the motor 18. Rotation of the pinion 54 of the output shaft 58causes the input gear 50 to rotate. Rotation of the input gear 50 causesthe intermediate pinion 62 to rotate, which drives the output gear 66 onthe spindle 22, causing the spindle 22 and the tool bit 25 to rotate.

Rotation of the pinion 54 also causes the crank gear 78 to rotate aboutthe stationary shaft 82. Because the tool bit 25 is depressed againstthe workpiece, the spindle 22 is in the first position and the sensor122 detects that the washer 126 is proximate the sensor 122, such thatthe controller 31 allows the electromagnetic clutch mechanism 118 to bein the first state. Thus, the crank shaft 122 receives torque from thecrank gear 78, causing the crank shaft 122 and the eccentric pin 110 torotate about the central axis 86. If “hammer-drill” mode has beenselected, rotation of the eccentric pin 110 causes the piston 34 toreciprocate within the spindle 22 via the connecting rod 116, whichcauses the striker 38 to impart axial blows to the anvil 42, which inturn causes reciprocation of the tool bit 25 against a workpiece.Specifically, a variable pressure air pocket (or an air spring) isdeveloped between the piston 34 and the striker 38 when the piston 34reciprocates within the spindle 22, whereby expansion and contraction ofthe air pocket induces reciprocation of the striker 38. The impactbetween the striker 38 and the anvil 42 is then transferred to the toolbit 25, causing it to reciprocate for performing work on the workpiece.

During operation of the rotary hammer 10 in either the hammer-drill modeor drill-only mode, if the operator intentionally or inadvertentlyremoves the bit 25 from the workpiece, the spring biases the spindle 22to the second position, creating the gap G between the washer 126 andthe sensor 122. In response to the sensor 122 detecting that the washer126 is no longer proximate the sensor 122, the controller 31 switchesthe electromagnetic clutch mechanism 118 from the first state to thesecond state, such that the crank shaft 102 is no longer coupled forrotation with the crank gear 78, disabling the impact mechanism 32. Oncethe impact mechanism 32 is disabled, rotation of the crank shaft 102decelerates and ceases. Thus, reciprocation of the piston 34 ceases,such that reciprocation of the striker 38 ceases and the anvil 42 nolonger imparts axil impacts to the tool bit 25.

Use of the sensor 122 and controller 31 to switch the electromagneticclutch mechanism 118 from the first state to the second state to disablethe impact mechanism 32 provides many advantages. For example, thestriker 38 and anvil 42 can be formed as simple cylindrical components,instead of requiring more complex geometries that interface with othercomponents of the housing 14 or quick-release mechanism 24 to “park” orstop reciprocation of the striker 38 and anvil 42. Employing a simplecylindrical geometry for the striker 38 and anvil 42 reduces stressconcentrations that are associated with more complex geometries, suchthat the efficacy and longevity of the striker 38 and anvil 42 areimproved. Also, the striker 38 and anvil 42 can be made shorter, oncethey no longer need complex geometries to assist in the cessation oftheir respective reciprocation. Thus, using simple cylindricalcomponents for manufacturing the strike 38 and anvil 42 reduce theattendant manufacturing costs. Also, components of quick-releasemechanism 24 have increased longevity because incidences of the bit 25being forced forward by the anvil 42 are reduced with use of the sensor122 and controller 31. Also, decompression vents in the spindle 22 thatassist in decompressing the spindle 22 after the impact mechanism 32 isdisabled can be removed with use of the sensor 122 and controller 31.

FIGS. 4A-4E show the electromagnetic clutch mechanism 118 of FIG. 1 ingreater detail. In particular, the electromagnetic clutch mechanism 118of FIG. 1 is an electromagnetic friction clutch arranged between thecrank gear 78 and the crank shaft 102.

The crank gear 78 includes a body 400 that has a first end 404, a secondend 408 opposite the first end 404, a longitudinal axis 412 that extendsbetween the first end 404 and the second end 408, and a plurality ofgear teeth 78 a extending from an exterior wall thereof. The pluralityof gear teeth 78 a mesh with the teeth of the pinion gear 54. The firstend 404 defines a bore 416 extending therethrough. The stationary shaft82 extends through the bore 416 and a bearing 420 (e.g., a ball bearing)is positioned between the stationary shaft 82 and the bore 416. The body400 has a first inner surface 424 that is recessed from the second end408 and a second inner surface 428 that is recessed relative to thefirst inner surface 424. The crank gear 78 includes a plurality of teethor projections 432, each of the plurality of projections 432 extendradially inward from an interior wall 436. The projections 432 arearranged circumferentially around the interior wall 436 and are evenlyspaced relative to one another. The projections 436 are positioned on(or otherwise adjacent to) the first inner surface 424. In theillustrated embodiment, there are four projections 432, but in otherembodiments, there may be greater or fewer than four projections 432. Atapered surface 440 extends between the first inner surface 424 and thesecond inner surface 428. Accordingly, the second inner surface 428 andthe tapered surface 440 define a frusto-conical recess.

The crank shaft 102 includes a body 450 that has first end 454, a secondend 458 opposite the first end 454, and a longitudinal axis 462 thatextends between the first end 454 and the second end 458. A firstportion 466 extends from the first end 454 towards the second end 458and a second portion 470 extends from the first portion 466 to thesecond end 458. The first portion 466 has an outer surface with splines474 (FIG. 4C). A flange 478 extends from the outer surface and ispositioned adjacent the splines 474. With respect to FIG. 4C, the secondportion 470 has a first end 482 and a second end 486 that is oppositethe first end 482. The first end 482 is narrower than the second end 486such that the second portion 470 defines an oblong shape. The crank pin110 extends from the first end 82 and is oriented parallel with thelongitudinal axis 462. A bore 492 extends through the first and secondportions 466, 470 of the crank shaft 102 and is positioned centrallybetween the first end 454 and the second end 458. The bore 492 includesa first inner dimension (e.g., a first inner diameter) extending alongthe first portion 466 and the bore 492 includes a second inner dimension(e.g., a second inner diameter) extending along at least a portion ofthe first portion 466. The second inner dimension is smaller than thefirst inner dimension. The portion of the bore 492 extending through thecrank shaft 102 is configured to receive the stationary shaft 82 and abearing 496 is positioned between the stationary shaft 82 and the bore492 in the first portion 466. The flange 78 is spaced apart from thesecond portion 470.

As shown in FIGS. 4B and 4C, the electromagnetic friction clutch 118includes a plunger or coupler 500, a biasing member 504 (e.g., aspring), and an electromagnet 508 (FIG. 4B). The plunger 500 includes abody 510 that has a first end 512, a second end 516 opposite the firstend 512, and a longitudinal axis 520 that extends between the first end512 and the second end 516. The plunger 500 includes permanent magnetsor is at least partially formed of a ferromagnetic material. A firstportion 526 is positioned at or adjacent the first end 512 and extendstowards the second end 516. A second portion 530 extends from the firstportion 526 towards the second end 516. The first portion 526 has afirst dimension (e.g., a first diameter) and the second portion 530 hasa second dimension (e.g., a second diameter) that is smaller than thefirst dimension. The first portion 526 has a frusto-conical shape.Therefore, the first portion 530 defines an outer surface 534 that istapered along the longitudinal axis 520 in a direction toward the firstend 512. The first portion 526 further includes a plurality of teeth orprojections 538 extending therefrom. In the illustrated embodiment, eachof the plurality of projections 538 extend radially outwardly from awidest point of the first portion 526 and are evenly spaced about acircumference of the first portion 526. In the illustrated embodiment,there are four projections 538, but in other embodiments, there may begreater or fewer than four projections 538. In some embodiments, thereis a groove positioned in a surface of the first portion 526 andsurrounds the second portion 530. The second portion 530 issubstantially cylindrical. A bore 546 extends along the longitudinalaxis 520 (through both portions 526, 530) from the first end 512 to thesecond end 516. At least a portion of the bore 546 has splines 548(FIGS. 4C-4E).

The first portion 466 of the crank shaft 102 is received in the bore 546of the second portion 530 of the plunger 500, causing the splines 474,548 on the crank shaft 102 and the plunger 500, respectively, to engage.The spline connection between the crank shaft 102 and the plunger 500ensures that the crank shaft 102 provides torque through the plunger500. The biasing member 504 is positioned between the first portion 466of the plunger 500 and the flange 478 of the crank shaft 102. Thebiasing member 504 may be seated within the groove, when present, of thefirst portion 526 of the plunger 500 and is positioned about the secondportion 530 of the plunger 500. A biasing force of the biasing member504 is directed away from the crank shaft 102 and toward the firstportion 526 of the plunger 500 (and the crank gear 78).

The plunger 500 is selectively coupled to the crank gear 78 forco-rotation therewith. The first portion 526 of the plunger 500 isconfigured to be selectively received, supported by, and rotatable withthe crank gear 78. In particular, the first portion 526 of the plunger500 is configured to be matingly received by the second inner surface428 of the crank gear 78. Therefore, the tapered surface 534 of thefirst portion 526 of the plunger 500 is seated adjacent or against thetapered surface 440 between the first and second inner surfaces 424,428, and the plurality of projections 538 of the first portion 526 ofthe plunger 500 are supported by the first inner surface 424 of thecrank gear 78. The stationary shaft 82 extends through the aligned bores416, 492, 546 of the crank gear 78, the plunger 500, and the crank shaft102 such that the axes 412, 462, 520 thereof are aligned (e.g.,coincident with one another). A washer or other retaining device 550(FIG. 4B) may be positioned between the crank gear 78 and either or bothof the crank shaft 102 or plunger 500.

The electromagnet 508 is positioned between the crank gear 78 and thecrank shaft 102. In this embodiment, the electromagnet 508 is positionedadjacent the flange 478 of the crank shaft 102 and is spaced apart fromthe crank gear 78. The electromagnet 508 is substantially cylindricaland includes a bore 554. The bore 554 is sized and shaped such that theplunger 500 and biasing member 504 extend therethrough.

The plunger 500 is configured to selectively couple the crank gear 78and the crank shaft 102 for co-rotation. Thus, in the embodiment ofFIGS. 4A-4E, in the first state of the electromagnetic clutch mechanism118, the electromagnet 508 is de-energized to cause the crank gear 78and crank shaft 102 to frictionally engage with each other (i.e., viathe plunger 500), such that the crank gear 78 and crank shaft 102 arecoupled for co-rotation. During normal operation, as shown in FIG. 4D,the electromagnet 508 is de-energized such that the electromagneticclutch mechanism 118 is off. Accordingly, the biasing member 504 biasesthe plunger 500 toward the crank gear 78 to frictionally engage theplunger 500 to the crank gear 78 (via the tapered surfaces 440, 534).

Moreover, during normal operation, the reaction torque applied to thecrank shaft 102 is relatively high when the crank shaft 102 is rotatingin a “forward direction” (i.e., coinciding with movement of the piston34 from its rearward-most position within the spindle 22 to itsforward-most position, when the trapped air between the piston 34 andthe striker 38 is being compressed) and the reaction torque applied tothe crank shaft 102 is relatively low when the crank shaft 102 isrotating in a “reverse direction” (i.e., coinciding with movement of thepiston 34 from its forward-most position within the spindle 22 to itsrearward-most position, when the trapped air between the piston 34 andthe striker 34 is permitted to expand). To prevent any slippage betweenthe respective tapered surfaces 440, 534 of the crank gear 78 and theplunger 500 during rotation of the crank shaft 102 in the forwarddirection, each of the projections 538 of the plunger 500 engages one ofthe projections 432 of the crank gear 78 to transfer torque from thecrank gear 78 to the crank shaft 102.

When the rotary hammer 10 needs to park and stop hammering, the sensor122 detects that the washer 126 is no longer proximate the sensor 122and the controller 31 switches the electromagnetic clutch mechanism 118from the first state to the second state. In the embodiment of FIGS.4A-4E, in the second state of the electromagnetic clutch mechanism 118,the electromagnetic clutch 118 is turned on such that the electromagnet508 is energized. This generates a magnetic force that overcomes thebiasing force of the biasing member 504, pulling the plunger 500 upwardfrom the frame of reference of FIG. 4B to disengage the plunger 500 (andtherefore the crank shaft 102) from the crank gear 78 as shown in FIG.4E. Accordingly, the crank shaft 102 is no longer coupled forco-rotation with the crank gear 78. Thus, the piston 34, and thereforethe striker 38, stop reciprocating.

When the sensor 122 detects that the washer 126 is once again proximateto the sensor 122, the controller 31 switches the electromagnetic clutchmechanism 118 from the second state back to the first state, which turnsthe electromagnetic clutch 118 off again. The biasing member 504rebounds, re-engaging the plunger 500 with the crank gear 78 such thatthe crank gear 78 and crank shaft 102 once again frictionally engagewith each other. The projections 538 of the plunger 500 are spaced apartfrom one another so the plunger 500 can fall between the projections 432of the crank gear 78. In the unlikely event that the projections 538 ofthe plunger 500 hit the projections of the crank gear 78, the plunger500 will slip until it can quickly fall between adjacent projections 432of the crank gear 78.

FIGS. 5A-5F show an electromagnetic clutch mechanism 118 a according toanother embodiment. The electromagnetic clutch of FIGS. 5A-5F is similarto the electromagnetic clutch of FIGS. 4A-4E so like structure will beidentified with like reference numerals and only the differences will bediscussed herein.

The crank gear 78 of FIGS. 5A-5F includes an inner surface 570 that isrecessed relative to second end 408. A plurality of grooves 574 aredefined in the interior wall 436 of the body 400 and positioned adjacentthe recessed inner surface 570. In the illustrated embodiment, each ofthe plurality of grooves 574 is V-shaped with a vertex of the groove 574positioned radially outward from an opening of the groove 574.

As shown in FIGS. 5B-5E a carrier 580 is positioned within crank gear78. The carrier 580 includes a support surface 584 and circumferentialwall 588. The support surface 584 includes a first surface 592 that ispositioned adjacent the first portion 466 of the crank shaft 102 and asecond surface 596 that is recessed relative to the first surface 592.The circumferential wall 588 is coupled to and extends from the supportsurface 584, and second surface 596 defines a groove. In the illustratedembodiment, the circumferential wall 588 extends from the supportsurface 584 at a non-perpendicular angle (e.g., an oblique angle).Accordingly, the circumferential wall 588 defines a tapered surface orfrusto-conical shape. The circumferential wall 588 includes a pluralityof apertures 600 therethrough. Each of the apertures 600 receives adetent 604 (e.g., a ball). In some embodiments, such as FIG. 5A-5E, theapertures 600 may be substantially circular to accommodate the sphericaldetents 604. In some embodiments, such as in FIG. 5F, the apertures 600may be elongated or oblong to accommodate cylindrical (e.g., pin-shaped)detents 604. The carrier 580 maintains the circumferential spacing ofthe detents 604 and retains the detents 604 to the plunger 500.Moreover, in some embodiments, the carrier 580 may be integrally coupledto or adjacent the first end of either the crank shaft 102 or theplunger 500.

The first portion 466 of the crank shaft 102 is received in the bore 546of the second portion 530 of the plunger 500, and the carrier 580 ispositioned adjacent the first portion 526 of the plunger 500. Inparticular, a portion of the plunger 500 is received in the groove ofthe support surface 584 of the carrier 580. As shown, the taperedsurfaces of the cylindrical wall 588 of the carrier 580 and the firstportion 526 of the plunger 500 are substantially the same. Moreover, thedetents 604 are positioned between and movable relative to the carrier580 and the plunger 500, and specifically, between the tapered surfacesof the carrier 580 and the plunger 500. Like the embodiment of FIGS.4A-4E, in the embodiment of FIGS. 5A-5F, a spline-fit is created betweenthe crank shaft 102 and the plunger 500 as a result of the matingsplines 474, 548. The carrier 580 is positioned adjacent the recessedinner surface 570 of the crank gear 78 such that each of the detents 604of the crank shaft 102 are selectively received in a respective groove574 in the crank gear 78.

The plunger 500 is configured to selectively couple the crank gear 78and the crank shaft 102 for co-rotation therewith. Thus, in theembodiment of FIGS. 5A-5F, in the first state of the electromagneticclutch mechanism 118 a, the electromagnet 508 is de-energized to causethe crank gear 78 and crank shaft 102 to frictionally engage with eachother (e.g., via the plunger 500 and the carrier 580), such that thecrank gear 78 and crank shaft 102 are coupled for co-rotation. Duringnormal operation, the electromagnet 508 is de-energized such that theelectromagnetic clutch mechanism 118 a is off. Accordingly, the biasingmember 504 biases plunger 500 toward the carrier 580 of the crank shaft102 to frictionally engage the plunger 500 to the crank gear 78 (viatapered surface 534 and the surfaces of the detents 604).

Moreover, as noted above, during normal operation, the reaction torqueapplied to the crank shaft 102 is relatively high when the crank shaft102 is rotating in the forward direction and the reaction torque appliedto the crank shaft 102 is relatively low when the crank shaft 102 isrotating in the reverse direction. To prevent any slippage between thetapered surface 534 of the plunger 500 and the detents 604 of thecarrier 580 during rotation of the crank shaft 102 in the forwarddirection, each of the detents 604 of the carrier 570 engages one of thegrooves 574 of the crank gear 78 to transfer torque from the crank gear78 to the crank shaft 102

When the rotary hammer 10 needs to park and stop hammering, the sensor122 detects that the washer 126 is no longer proximate the sensor 122and the controller 31 switches the electromagnetic clutch mechanism 118a from the first state to the second state. In the embodiment of FIGS.5A-5F, in the second state of the electromagnet clutch mechanism 118 a,the electromagnetic clutch 118 a is turned on such that theelectromagnet 508 is energized. This generates a magnetic force thatovercomes the biasing force of the biasing member 504, pulling theplunger 500 upward from the frame of reference of FIG. 5B to disengagethe plunger 500 (and therefore the crank shaft 102) from the carrier580, and therefore the crank gear 78, as shown in FIG. 5E. That is, thetapered surface of the first portion 526 of the plunger 500 disengagesfrom the detents 604. When plunger 500 is biased away from the carrier580, the tapered surface 534 of the first portion 526 of the plunger 500moves away from carrier 580 and the detents 604 move radially inward andout of engagement with the grooves 574 of the crank gear 78.Accordingly, the crank shaft 102 is no longer coupled for co-rotationwith the crank gear 78. Thus, the piston 34, and therefore the striker38, stops reciprocating.

When the sensor 122 detects that the washer 126 is once again proximateto the sensor 122, the controller 31 switches the electromagnetic clutchmechanism 118 a from the second state back to the first state, whichturns the electromagnetic clutch 118 a off again. The biasing force ofthe biasing member 504 rebounds, re-engaging the plunger 500 with thecarrier 580 such that the crank gear 78 and crank shaft 102 once againfrictionally engage with each other.

In each of the embodiments of FIGS. 4A-4E and 5A-5F, the electromagnet508 is off when the electromagnetic clutch mechanism 118, 118 a is inthe first state and the electromagnet 508 is on when the electromagneticclutch mechanism 118, 118 a is in the second state. In otherembodiments, however, the electromagnet 508 may be on when theelectromagnetic clutch mechanism 118, 118 a is in the first state andthe electromagnet 508 may be off when the electromagnetic clutchmechanism 118, 118 a is in the second state. In this case, the bias ofthe biasing member 504 would be opposite that of FIGS. 4A-4E and 5A-5F.In other words, the bias of the spring would be away from the crank gear78 (and plunger 500) and toward the crank shaft 102. Moreover, in thiscase, the electromagnet 508 would be positioned adjacent the crank gear78 and would be spaced apart from the flange 478 of the crank shaft 102.Accordingly, when the electromagnetic clutch mechanism 118, 118 a is on(and the magnet is energized), a force overcomes the biasing force ofthe biasing member 504 to cause the crank gear 78 and crank shaft 102 tofrictionally engage with each other (via the plunger 500), such that thecrank gear 78 and crank shaft 102 are coupled for co-rotation. When theelectromagnetic clutch 118, 118 a is on (and the magnet is energized),the bias of the biasing member 504 moves causes the crank gear 78 todisengage from the crank shaft 102 such that the crank shaft 102 is nolonger coupled for co-rotation with the crank gear 78.

In another embodiment of an electromagnet clutch mechanism 118 b shownin FIGS. 6 and 7, the crank shaft 102 includes a plurality of balls 140(e.g. steel balls) retained by a plate 142. The electromagnetic clutchmechanism 118 b includes a coupler 144 arranged between the crank gear78 and the crank shaft 102 and biased toward the crank shaft 102 by aconical spring 146 that is coupled to the crank gear 78. The coupler 144includes permanent magnets or is at least partially formed of aferromagnetic material. The coupler 144 includes a plurality of recesses148 configured to receive the balls 140. The coupler 144 is biased bythe spring 146 toward a first position (FIG. 6) in which the coupler 144is in contact with the crank shaft 102, such that the balls 140 arereceived in the recesses 148, thus enabling torque to be transferredfrom the crank gear 78 to the crank shaft 102 (via the spring 146 andthe coupler 144). When the electromagnetic clutch mechanism 118 b isswitched from the first state to the second state, the coupler 144 ismoved against the biasing force of the spring 146 and away from thecrank shaft 102 to a second position (FIG. 7), in which the balls 140are no longer in the recesses 148. Thus, when the coupler 144 is in thesecond position, torque is no longer transferred from the crank gear 78to the crank shaft 102. Therefore, reciprocating movement of the piston34, and therefore the striker 38, stops.

In yet another embodiment of an electromagnet clutch mechanism 118 cshown in FIGS. 8 and 9, the crank gear 78 includes recesses 134 and thecrank shaft 102 includes teeth 136 configured to be engaged with therecesses 134. The crank shaft 102 includes permanent magnets or is atleast partially formed of a ferromagnetic material. As shown in FIG. 7,in the first state of the electromagnetic clutch mechanism 118 c, theelectromagnet is de-energized and a biasing member 146 (shownschematically, e.g., a spring) biases the crank shaft 102 toward thecrank gear 78, such that the teeth 136 are engaged with the recesses 134and the crank shaft 102 receives torque from the crank gear 78. As shownin FIG. 9, in the second state of the electromagnetic clutch mechanism118 c, the electromagnet is energized, which pulls the crank shaft 102away from the crank gear 78 to disengage the teeth 136 from the recesses134. In this position, the crank shaft 102 is no longer coupled forco-rotation with the crank gear 78. Therefore, reciprocating movement ofthe piston 34, and therefore the striker 38, stops.

In yet another embodiment of an electromagnet clutch mechanism 118 dshown in FIG. 10, the electromagnetic clutch mechanism 118 d includes anelectromagnet coupler 152 arranged on the stationary shaft 82 betweenthe crank gear 78 and the crank shaft 102. Each of the crank gear 78 andcrank shaft 102 includes permanent magnets. When the electromagneticclutch mechanism 118 d is in the first state, the electromagnet coupler152 is energized, thus drawing the crank gear 78 and crank shaft 102into engagement with the electromagnet coupler 152, such that the crankshaft 102 receives torque from the crank gear 78 via the electromagneticcoupler 152. When the electromagnetic clutch mechanism 118 d is switchedfrom the first state to the second state, the electromagnet coupler 152is de-energized, such that the crank gear 78 and crank shaft 102 are nolonger magnetically attracted to the electromagnet coupler 152, and theelectromagnet coupler 152 no longer transfers torque from the crank gear78 to the crank shaft 102. Therefore, reciprocating movement of thepiston 34, and therefore the striker 38, stops.

In yet another embodiment of an electromagnet clutch mechanism 118 eshown in FIGS. 11 and 12, the electromagnetic clutch mechanism 118 eincludes a coupler 234 arranged between the crank gear 78 and the crankshaft 102. The coupler 234 includes one or more pieces 238 includingpermanent magnets or formed of a ferromagnetic material. In the firststate of the electromagnetic clutch mechanism 118 e, the coupler 234transfers torque from the crank gear 78 to the crank shaft 102. When theelectromagnetic clutch mechanism 118 e is switched from the first stateto the second state, the electromagnet is energized and causes thepieces 238 to move from a first position to a second position, in whichthe coupler 234 contracts in the axial or radial direction, such thattorque is no longer is transferred from the crank gear 78 to the crankshaft 102. Therefore, reciprocating movement of the piston 34, andtherefore the striker 38, stops.

In yet another embodiment of an electromagnet clutch mechanism 118 fshown in FIG. 13, the electromagnetic clutch mechanism 118 f includes acoupler 242 arranged between the crank gear 78 and the crank shaft 102and filled with a ferrofluid (e.g., therafluid or oil). Theelectromagnetic clutch mechanism 118 f also includes a coil 246 (shownschematically) surrounding the coupler 242. In the first state of theelectromagnetic clutch mechanism 118 f, the coil 246 is energized,causing the ferrofluid to become more viscous, such that the coupler 242transfers torque from the crank gear 78 to the crank shaft 102. In someembodiments, the ferrofluid becomes solid when the coil 246 around thecoupler 242 is energized. In the second state of the electromagneticclutch mechanism 118 f, the coil 246 is de-energized, such that theferrofluid becomes less viscous, and thus the coupler 242 no longertransfers torque from the crank gear 78 to the crank shaft 102.Therefore, reciprocating movement of the piston 34, and therefore thestriker 38, stops.

In yet another embodiment of an electromagnet clutch mechanism 118 gshown in FIG. 14, the crank gear 78 and crank shaft 102 are integrallyformed as one unit, and the eccentric pin 110 is replaced with amoveable pin 110 a that is moveable relative to the crank shaft 102between a first, eccentric, position (FIGS. 1 and 14) and a second,in-line position, in which the moveable pin 110 a is coaxial with thecentral axis 86. The moveable pin 110 a includes permanent magnets or isat least partially formed of a ferromagnetic material. When theelectromagnetic clutch mechanism 118 g is in the first state, anelectromagnet (not shown) is de-energized, allowing the moveable pin 110a to be biased toward the first, eccentric, position, such that themoveable pin 110 a rotates eccentrically about the central axis 86,causing the connecting rod 116 to move forward and back to reciprocatethe piston 34. However, when the electromagnetic clutch mechanism 118 gis switched from the first state to the second state, the electromagnetis energized to move the moveable pin 110 a radially inward, asindicated by arrow A, and hold the moveable pin 110 a in the secondposition. Once the moveable pin 110 a has moved to the second position,even though the crank shaft 102 continues to rotate about the centralaxis 86, because the moveable pin 110 a is coaxial with the central axis86, the moveable pin 110 a no longer eccentrically rotates about thecentral axis 86. Rather, the moveable pin 110 a rotates in a coaxialmanner about the central axis 86. Thus, reciprocation of the piston 34ceases, as the connecting rod 116 is no longer moved forward andrearward by the moveable pin 110 a. Thus, the piston 34 and striker 38stop reciprocating.

In yet another embodiment of an electromagnet clutch mechanism 118 hshown in FIG. 15, the electromagnetic clutch mechanism 118 h includes acoil 250 in the stationary shaft 82 and the crank shaft 102 includespermanent magnets or is at least partially formed of a ferromagneticmaterial. When the electromagnetic clutch mechanism 118 h is in thefirst state, the coil 250 is de-energized and the crank shaft 102 isengaged with the crank gear 78 to receive torque therefrom. When theelectromagnetic clutch mechanism 118 h is switched from the first stateto the second state, the coil 250 is energized and thus moves the crankshaft 102 away from the crank gear 78, such that the crank shaft 102 nolonger receives torque from the crank gear 78.

In an embodiment shown in FIG. 16, instead of an electromagnetic clutchmechanism 118, a one-way bearing 132 is arranged between the crank gear78 and the crank shaft 102. During normal operation, the motor 18 isrotating in a first direction and the one-way bearing 132 transferstorque from the crank gear 78 to the crank shaft 102. However, inresponse to the sensor 122 detecting that the washer 126 is no longerproximate the sensor 122, the controller 31 reverses the direction ofthe motor 18, such that it is rotating in a second direction that isopposite the first direction. Thus, the one-way bearing 132 no longertransfers torque from the crank gear 78 to the crank shaft 102.Therefore, the piston 34 and striker 38 stop reciprocating.

In an embodiment shown in FIG. 17, the electromagnetic clutch mechanism118 is omitted. And, instead of using the crank gear 78, a planetarygear set 254 (shown schematically) receives torque from the pinion 54 ofthe output shaft 58 of the motor 18. In a first state of the planetarygear set 254, the planetary gears transfer torque to the crank shaft102. In a second state of the planetary gear set 254, the planetarygears are shifted, such that torque is no longer transferred from theplanetary gear set 254 to the crank shaft 102.

In an embodiment shown in FIGS. 18-20, the electromagnetic clutchmechanism 118 is omitted, and the spindle 22 includes a plurality oflongitudinal recesses 258, with each recess 258 including a plurality ofports 262. As shown in FIG. 20, a coupler 266 is arranged on the spindle22 and as shown in FIG. 19, the coupler 266 includes a plurality of legs270 that are arranged in the recesses 258 when the coupler 266 is in afirst position, described below. Specifically, during operation, when auser presses forward on a handle 272 (FIG. 1), the coupler 266 is movedto the position shown in FIG. 20, in which the legs 270 seal all theports 262 in the recesses 258 of the spindle 22. Thus, an interiorvolume 274 of the spindle 22 between the piston 34 and the striker 38 issealed, such that the variable pressure air pocket (or an air spring) isdeveloped between the piston 34 and the striker 38 when the piston 34reciprocates within the spindle 22, whereby expansion and contraction ofthe air pocket induces reciprocation of the striker 38. However, if theoperator releases the handle 272, intentionally or unintentionally, thecoupler 22 is biased forward such that it moves relative to the spindle22 to a position in which the legs 270 no longer seal all of the ports262 in the recesses 258 of the spindle 22. Thus, even though piston 34will continue to reciprocate, a variable pressure air pocket will not becreated because air is permitted to enter and escape the interior volume274 via the ports 262. Thus, the interior volume 274 is maintained atapproximately atmospheric pressure, such that reciprocation of thestriker 38 is not induced, thereby ceasing reciprocation of the bit 25.

In an embodiment shown in FIG. 21, the piston 34 includes a through bore278 that extends from a front end 282 to a rear end 286 of the piston34. The electromagnetic clutch mechanism 118 is omitted and replacedwith an electromagnetic mechanism 288 arranged proximate the piston 34.When the electromagnetic mechanism 288 is in a first state, a solenoid289 is de-energized and a plug 290 is biased to a first position (FIG.21), in which it seals the through bore 278. Therefore, because theinterior volume 274 is sealed, the variable pressure air pocket (or anair spring) is developed between the piston 34 and the striker 38 whenthe piston 34 reciprocates within the spindle 22, whereby expansion andcontraction of the air pocket induces reciprocation of the striker 38.However, when the electromagnetic mechanism 288 is switched from thefirst state to the second state in response to the sensor 122 detectingthat the washer 126 is no longer proximate the sensor 122, the solenoid289 is energized to move the plug 290 from the first position to asecond position, in which the through bore 278 is unsealed, such thatthe interior volume 274 is maintained at approximately atmosphericpressure via fluid communication with the atmosphere through the throughbore 278. Therefore, reciprocation of the striker 38 is not induced inresponse to reciprocation of the piston 34, thereby ceasingreciprocation of the bit 25. In a variation of the embodiment of FIG.21, when the electromagnetic mechanism 288 is in the first state, thesolenoid 289 is energized to move the plug 290 to the first position,and when the electromagnetic mechanism 288 switches to the second state,solenoid 289 is de-energized, allowing the plug 290 to be biased to thesecond position.

In an embodiment shown in FIG. 22, the spindle 22 includes a pluralityof ports 294 and the electromagnetic clutch mechanism 118 is omitted andreplaced with the electromagnetic mechanism 288 arranged on the spindle22. The electromagnetic mechanism 288 includes a coupler 298 arranged onthe spindle 22 to selectively cover the ports 294. Specifically, whenthe electromagnetic mechanism 288 is in the first state, a solenoid 299is de-energized and the coupler 298 is therefore biased to a firstposition shown in FIG. 21 in which the coupler 298 is axially alignedwith the ports 294, thus sealing all the ports 294. Thus, the interiorvolume 274 of the spindle 22 between the piston 34 and the striker 38 issealed, such that the variable pressure air pocket (or an air spring) isdeveloped between the piston 34 and the striker 38 when the piston 34reciprocates within the spindle 22, whereby expansion and contraction ofthe air pocket induces reciprocation of the striker 38. However, whenthe electromagnetic mechanism 288 is switched from the first state tothe second state in response to the sensor 122 detecting that the washer126 is no longer proximate the sensor 122, the solenoid 299 is energizedto move the coupler 298 to a second position in which the ports 294 areno longer sealed by the coupler 294. Thus, even though piston 34 willcontinue to reciprocate, a variable pressure air pocket will not becreated because air is permitted to enter and escape the interior volume274 via the ports 294. Thus, the interior volume 274 is maintained atapproximately atmospheric pressure, such that reciprocation of thestriker 38 is not induced, thereby ceasing reciprocation of the bit 25.

In an embodiment shown in FIG. 23, the output shaft 58 of the motor 18includes a first part 306 and a second part 310 that selectivelyreceives torque from the first part 306 and transfers it to the crankgear 78 and the input gear 50. Instead of being arranged proximate thecrank gear 78 and the crank shaft 102, the electromagnetic clutchmechanism 118 is arranged between the first and second parts 306, 310 ofthe output shaft 58. In some embodiments, the first and second parts306, 310, and the electromagnetic clutch 118 are arranged and configuredas described in the embodiment of FIGS. 1-5 of the '716 Application. Insome embodiments, the first and second parts 306, 210 and theelectromagnetic clutch 118 are arranged and configured as described inthe embodiment of FIGS. 8 and 9 of the '716 Application or FIGS. 4A-5Fof the present application described above. In the first state of theelectromagnetic clutch mechanism 118, an electromagnet is de-energizedand the second part 310 is biased into frictional engagement with thefirst part 306 of the output shaft 58, such that the second part 310receives torque from the first part 306 and transfers torque to theinput gear 50 and crank gear 78, thus causing rotation of the spindle 22and reciprocation of the piston 34. However, when the electromagneticclutch mechanism 118 is switched from the first state to the secondstate in response to the sensor 122 detecting that the washer 126 is nolonger proximate the sensor 122, the electromagnet is energized to movethe second part 310 away from the first part 306, such that the secondpart 310 no longer receives torque from the first part 306. Thus, thesecond part 310 ceases to transfer torque to the input gear 50 and thecrank gear 78, and the piston 34 and bit 25 both stop reciprocating.

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of one or more independent aspects of the inventionas described.

Various features and advantages are set forth in the following claims.

What is claimed is:
 1. A rotary hammer adapted to impart axial impactsto a tool bit, the rotary hammer comprising: a housing; a motorsupported by the housing; a spindle coupled to the motor for receivingtorque from the motor, causing the spindle to rotate; a reciprocationmechanism operable to create a variable pressure air spring within thespindle; an anvil received within the spindle for reciprocation inresponse to the pressure of the air spring, the anvil imparting axialimpacts to the tool bit; a bit retention assembly for securing the toolbit to the spindle; and an electromagnetic clutch mechanism switchablebetween a first state, in which the reciprocation mechanism is enabled,such that the anvil imparts axial impacts to the tool bit, and a secondstate, in which the reciprocation mechanism is disabled, such that theanvil ceases to impart axial impacts to the tool bit.
 2. The rotaryhammer of claim 1, further comprising: a detectable member on thespindle; a sensor on the housing and configured to detect whether thedetectable member is proximate or not proximate the sensor; and acontroller configured to switch the electromagnetic clutch mechanismfrom the first state to the second state in response to the sensordetecting that the detectable member is not proximate the sensor,wherein the spindle is moveable between a first position, in which thesensor detects that the detectable member is proximate the sensor, and asecond position, in which the sensor detects that the detectable memberis not proximate the sensor, wherein the spindle is biased toward thesecond position.
 3. The rotary hammer of claim 2, wherein the detectablemember is a washer.
 4. The rotary hammer of claim 2, wherein thereciprocation mechanism includes a piston disposed within the spindle, acrank gear receiving torque from the motor, and a crank shaft configuredto reciprocate the piston within the spindle to create the variablepressure air spring in response to receiving torque from the crank gear,and wherein the electromagnetic clutch mechanism is positioned betweenthe crank gear and the crank shaft.
 5. The rotary hammer of claim 4,wherein when the electromagnetic clutch mechanism is in the first state,the crank shaft receives torque from the crank gear, such that the anvilimparts axial impacts to the tool bit, and wherein when theelectromagnetic clutch mechanism is in the second state, the crank shaftdoes not receive torque from the crank gear, such that the anvil ceasesto impart axial impacts to the tool bit.
 6. The rotary hammer of claim2, wherein the motor includes an output shaft having a first part and asecond part that selectively receives torque from the first part via theelectromagnetic clutch mechanism.
 7. A rotary hammer adapted to impartaxial impacts to a tool bit, the rotary hammer comprising: a housing; amotor supported by the housing; a spindle coupled to the motor forreceiving torque from the motor, causing the spindle to rotate; areciprocation mechanism operable to create a variable pressure airspring within the spindle, the reciprocation mechanism including apiston disposed within the spindle, a crank gear receiving torque fromthe motor, and a crank shaft configured to reciprocate the piston withinthe spindle to create the variable pressure air spring in response toreceiving torque from the crank gear, an anvil received within thespindle for reciprocation in response to the pressure of the air spring,the anvil imparting axial impacts to the tool bit; a bit retentionassembly for securing the tool bit to the spindle; and anelectromagnetic clutch mechanism switchable between a first state, inwhich the crank shaft receives torque from the crank gear, such that theanvil imparts axial impacts to the tool bit, and a second state, inwhich the crank shaft does not receive torque from the crank gear, suchthat the anvil ceases to impart axial impacts to the tool bit.
 8. Therotary hammer of claim 7, further comprising: a detectable member on thespindle; a sensor on the housing and configured to detect whether thedetectable member is proximate or not proximate the sensor; and acontroller configured to switch the electromagnetic clutch mechanismfrom the first state to the second state in response to the sensordetecting that the detectable member is not proximate the sensor,wherein the spindle is moveable between a first position, in which thesensor detects that the detectable member is proximate the sensor, and asecond position, in which the sensor detects that the detectable memberis not proximate the sensor, wherein the spindle is biased toward thesecond position.
 9. The rotary hammer of claim 7, wherein theelectromagnetic clutch includes a plunger that is coupled to the crankshaft for co-rotation therewith, and an electromagnet configured toselectively move the plunger relative to the crank shaft to selectivelyrotationally couple the crank shaft to the crank gear.
 10. The rotaryhammer of claim 9, wherein when the electromagnetic clutch mechanism isin the first state, the plunger is engaged with the crank gear, andwherein when the electromagnetic clutch mechanism is in the secondstate, the plunger is disengaged from the crank gear.
 11. The rotaryhammer of claim 10, wherein the plunger includes one or more projectionsextending radially therefrom, each of the one or more projections of theplunger configured to engage a projection of the crank gear, when theelectromagnetic clutch mechanism is in the first state, to transfertorque from the crank gear to the plunger and the crank shaft.
 12. Therotary hammer of claim 9, wherein when the electromagnetic clutchmechanism is in the first state, a detent mechanism engages both thecrank gear and the plunger to couple the crank gear and the plunger forco-rotation, and wherein when the electromagnetic clutch mechanism is inthe second state, the detent mechanism disengages at least one of thecrank gear or the plunger to prevent torque transfer between the crankgear and the plunger.
 13. The rotary hammer of claim 9, wherein theplunger includes a conical portion configured to frictionally engage amating conical portion of the crank gear when the electromagnetic clutchmechanism is in the first state.
 14. The rotary hammer of claim 9,wherein the plunger is biased into the first state, and wherein theelectromagnet is energized to disengage the plunger from the crank gear.15. The rotary hammer of claim 14, wherein the plunger is biased intothe first state by a compression spring.
 16. A rotary hammer adapted toimpart axial impacts to a tool bit, the rotary hammer comprising: ahousing; a motor supported by the housing; a spindle coupled to themotor for receiving torque from the motor, causing the spindle torotate; a reciprocation mechanism operable to create a variable pressureair spring within the spindle, the reciprocation mechanism including apiston disposed within the spindle, a crank gear receiving torque fromthe motor, and a crank shaft configured to reciprocate the piston withinthe spindle to create the variable pressure air spring in response toreceiving torque from the crank gear, an anvil received within thespindle for reciprocation in response to the pressure of the air spring,the anvil imparting axial impacts to the tool bit; a bit retentionassembly for securing the tool bit to the spindle; a port in one of thespindle or the piston; and a closure member that is movable relative tothe port between a first position, in which the closure member seals theport and an interior volume of the spindle between the piston the anvilis sealed to develop the variable pressure air spring, and a secondposition, in which the closure member is spaced apart from the port andthe interior volume of the spindle between the piston and the anvil isunsealed and unable to develop the variable pressure air spring.
 17. Therotary hammer of claim 16, wherein the port includes a plurality ofports arranged in a row along a length of the spindle, and wherein theclosure member is a coupler coupled to and movable relative to thespindle and having a leg that selectively covers the ports when thecoupler is in the first position.
 18. The rotary hammer of claim 17,wherein the coupler is biased into the second position.
 19. The rotaryhammer of claim 16, wherein the port is a through bore that extendsthrough the piston, wherein the closure member is a plug that isreceived in the through bore in the first position and at leastpartially removed from the through bore in the second position.
 20. Therotary hammer of claim 16, wherein the port extends through the spindle,wherein the closure member is a coupler that blocks the port in thefirst position and at least partially uncovers the port in the secondposition, and wherein the coupler is biased into the first position.